1. Field of the Invention
The present invention relates generally to printing presses and more particularly to printing presses having printing sleeves that are placed on or removed from a cylinder with the aid of air or other fluid pressure.
2. Background of the Invention
Tubular-shaped printing sleeves, such as offset lithographic printing blankets described in U.S. Pat. No. 5,215,013, are placed and removed axially over a printing cylinder. As described with respect to a blanket in the '013 patent, air holes typically are located on a work side end of the blanket cylinder to provide pressure to the inside of the blanket as the blanket is removed or placed axially over the blanket cylinder.
However, blankets can become stuck when mounted for too long, as air pressure from the air holes can be blocked and not reach the gear side end of the cylinder. Moreover, the use of only one set of air holes on the work side end makes hole placement critical, or the sleeve will not inflate or expand at all. With improperly placed holes, the air may simply rush out of the work side end without inflating the gear side end.
Also, it may be desirable to place multiple blankets side-by-side over a single blanket cylinder. A single set of work side holes can inflate only one of the blankets at the work side, thus not permitting the other blankets closer to the gear side to be removed.
It has been attempted to place additional air holes along the length of the body of the printing cylinder. However, when the sleeve is in a partially removed or placed position, these air holes remain uncovered while the work side air holes are covered. A large pressure reduction results as the air rushes out the uncovered holes and the flow drops at the work side holes, thus making blanket placement or removal difficult or impossible. Thus the additional holes require the use of multiple plumbing fixtures, solenoids and valves to control the air flow properly. These features tend to be expensive and are complicated, especially because the cylinder must rotate.
In a 1981 textbook entitled, Beruehrungsfreie Dichtungen (Contactless Seals), the authors describe labyrinth seals, in which fluid flow can be blocked or reduced using vortices. In FIG. 3-56 at pages 174–176, the effect of placement of fins on air flow and vortex generation is shown. However, the use of these seals in printing machines or for printing cylinders is not discussed.